1. Field of the Invention
This invention relates generally to brushless rotary electrical motor/generator structures for producing an output voltage or mechanical power output in the form of rotational torque such as for use in rotating the wheel of a vehicle and propelling the vehicle; and more specifically, to a radial gap motor/generator wherein at least one thin annular array of magnets is mounted for rotation to a rotor in radially spaced relation to at least one thin annular induction structure fixedly arranged on a stationary stator. Even more particularly, the present invention is directed to a cooling arrangement or structure for transferring heat build-up and cooling the induction structure during operation of the motor/generator.
2. Description of Prior Art
In general, brushless electrical motors may be termed “axial gap” or “radial gap.” In each, magnets are mounted on a rotor and an induction structure, or electrical coils, are mounted on a stator. In the axial gap motor, the coils and magnets are in juxtaposed relation with one another on respective co-axial circles and in respective axially spaced planes. In the radial gap motor, the coils and magnets are in radially spaced juxtaposed relation with one another in respective co-axially disposed cylindrical planes.
Axial gap motors employing coil armatures and brush commutation have been in use since the late 1950's. In a conventional (brushed) DC motor, the brushes make mechanical contact with a set of electrical contacts on the rotor (called the commutator), forming an electrical circuit between the DC electrical source and the armature coil-windings. As the armature rotates on axis, the stationary brushes come into contact with different sections of the rotating commutator.
Brushless disc-type axial gap motors were later developed, employing rotating magnets, coil stators and electronic commutation. In such brushless motor, the electromagnets do not move; instead, the permanent magnets rotate and the armature remains static. This gets around the problem of how to transfer current to a moving armature.
The brushless axial gap motor offers several advantages over brushed DC motors, including higher efficiency and reliability, reduced noise, reduced maintenance, longer lifetime (no brush erosion), elimination of ionizing sparks from the commutator, and overall reduction of electromagnetic interference. The maximum power that can be applied to a brushless motor is exceptionally high, limited almost exclusively by heat, which can damage the coils and affect the strength of the magnets.
Accordingly, an arrangement for obviating the deleterious effects of heat and temperature build-up in the brushless motor during operation thereof would be desirable and is an object of this invention.
Brushless axial gap motors have been used in large numbers in audio and video tape recorders and computer disc drives. In such a motor, a magnetic rotor disc with alternating North/South pole pieces rotates above and/or below a plane containing several flat, stator coils lying adjacent one another. Current flowing in the conductor wires of the coils interacts with the alternating magnetic flux lines of the disc, producing Lorentz forces perpendicular to the radially directed conductors and thus tangential to the axis of rotation. While current flows through the entire coil, only the radial extending portions of the conductors (called the working conductors) contribute torque to the rotor. See, for example, U.S. Pat. Nos. 3,988,024; 4,361,776; 4,371,801; and 5,146,144. A variation of this arrangement is known in which the circumferential portions (nonworking conductors) of the wire-wound coils overlap each other. See, for example, U.S. Pat. Nos. 4,068,143; 4,420,875; 4,551,645; and 4,743,813. While this arrangement allows closer packing of the working conductors, it also requires that the gap between the rotor's magnets and flux return be about twice as thick as would be required for a single thickness of a non-overlapping coil, thus reducing the magnetic flux density and thus reducing the motor's efficiency.
In view of the these disadvantages in the above-mentioned prior art, Kessinger et al. U.S. Pat. No. 5,744,896, issued Apr. 28, 1998, the specification of which is specifically incorporated herein in its entirety, discloses a motor which employs an axial gap magnetic structure wherein complementary faces of the stator and rotor are disposed in axially spaced relation and each receives, respectively, a flat array of coil winding segments and a flat array of permanent magnets, the segments and magnets of which being arranged in angularly spaced side-by-side relation and extending radially relative to the rotor axis of rotation. The coil winding segments are alike and each is generally trapezoidal and forms a ring shaped structure and the segments overlap with one another to form a thin planar electromagnetic structure. Electrical wires are wound about the coil structures and the longer legs (or sides) of the trapezoidal shape form the working portions of the coil windings.
Kessinger proposed that the individual coils making up a coil array be flat and rectangular in shape to form a thin disc coil array so as to maximize the electromotive interaction for a motor/generator of a given diameter and maximize the torque, which may be produced by a motor, or the voltage produced by a generator.
While believed useful for the purposes then desired, certain problems are believed to remain in an axial gap arrangement. During operation and rotation of the rotor, an outward radial shearing force is placed on the securement between the permanent magnets and the rotor face. Because of these forces and possible adverse effects of heat build up during continued use, the magnets may break free. Additional bonding material may be needed to overcome such situation, possibly resulting in increased cost and size of the structure.
Further, Kessinger proposes that the individual flat shaped rectangular coil structures closely abut one another and that individual coils be overmolded with a moldable material to form a suitable ring of suitable structural integrity and heat tolerance. However, such configuration suggests that some mechanism be provided to tolerate but not transfer heat from the coils during performance their electrical motor function.
Accordingly, an object of this invention is provision of a brushless radial gap motor/generator structure wherein the respective arrays of magnets and coil windings are separated by a radial gap, wherein to minimize the outer dimensions of the resulting structure.
An object of this invention is provision of a brushless radial gap motor/generator structure that effectively obviates adverse effects occasioned by rotation of the rotor.